tree-optimization/114760 - check variants of >> and << in loop-niter

When recognizing bit counting idiom, include pattern "x * 2"
for "x << 1", and "x / 2" for "x >> 1" (given x is unsigned).

gcc/ChangeLog:
	PR tree-optimization/114760
	* tree-ssa-loop-niter.cc (is_lshift_by_1): New function
	to check if STMT is equivalent to x << 1.
	(is_rshift_by_1): New function to check if STMT is
	equivalent to x >> 1.
	(number_of_iterations_cltz): Enhance the identification
	of logical shift by one.
	(number_of_iterations_cltz_complement): Enhance the
	identification of logical shift by one.

gcc/testsuite/ChangeLog:
	PR tree-optimization/114760
	* gcc.dg/tree-ssa/pr114760-1.c: New test.
	* gcc.dg/tree-ssa/pr114760-2.c: New test.

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr114760-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr114760-1.c
new file mode 100644 (file)
index 0000000..9f10ccc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr114760-1.c
@@ -0,0 +1,69 @@
+/* PR tree-optimization/114760 */
+/* { dg-do compile } */
+/* { dg-require-effective-target clz } */
+/* { dg-require-effective-target ctz } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
+
+unsigned
+ntz32_1 (unsigned x)
+{
+  int n = 32;
+  while (x != 0)
+    {
+      n = n - 1;
+      x = x * 2;
+    }
+  return n;
+}
+
+unsigned
+ntz32_2 (unsigned x)
+{
+  int n = 32;
+  while (x != 0)
+    {
+      n = n - 1;
+      x = x + x;
+    }
+  return n;
+}
+
+unsigned
+ntz32_3 (unsigned x)
+{
+  int n = 32;
+  while (x != 0)
+    {
+      n = n - 1;
+      x = x << 1;
+    }
+  return n;
+}
+
+#define PREC (__CHAR_BIT__ * __SIZEOF_INT__)
+int
+nlz32_1 (unsigned int b) {
+    int c = PREC;
+
+    while (b != 0) {
+       b >>= 1;
+       c --;
+    }
+
+    return c;
+}
+
+int
+nlz32_2 (unsigned int b) {
+    int c = PREC;
+
+    while (b != 0) {
+       b /= 2;
+       c --;
+    }
+
+    return c;
+}
+
+/* { dg-final { scan-tree-dump-times "__builtin_ctz|\\.CTZ" 3 "optimized" } } */
+/* { dg-final { scan-tree-dump-times "__builtin_clz|\\.CLZ" 2 "optimized" } } */
\ No newline at end of file

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr114760-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr114760-2.c
new file mode 100644 (file)
index 0000000..e1b4c4b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr114760-2.c
@@ -0,0 +1,20 @@
+/* PR tree-optimization/114760 */
+/* { dg-do compile } */
+/* { dg-require-effective-target clz } */
+/* { dg-options "-O3 -fdump-tree-optimized" } */
+
+// Check that for signed type, there's no CLZ.
+#define PREC (__CHAR_BIT__ * __SIZEOF_INT__)
+int
+no_nlz32 (int b) {
+    int c = PREC;
+
+    while (b != 0) {
+       b /= 2;
+       c --;
+    }
+
+    return c;
+}
+
+/* { dg-final { scan-tree-dump-not "__builtin_ctz|\\.CLZ" "optimized" } } */
\ No newline at end of file

diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index 0fde07e626f514808216ab22eb55aa1ce7d11d26..92db9c72ee47976787d489940c221c85f9a68ddf 100644 (file)
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -2303,6 +2303,38 @@ build_cltz_expr (tree src, bool leading, bool define_at_zero)
   return call;
 }
 
+/* Returns true if STMT is equivalent to x << 1.  */
+
+static bool
+is_lshift_by_1 (gassign *stmt)
+{
+  if (gimple_assign_rhs_code (stmt) == LSHIFT_EXPR
+      && integer_onep (gimple_assign_rhs2 (stmt)))
+    return true;
+  if (gimple_assign_rhs_code (stmt) == MULT_EXPR
+      && tree_fits_shwi_p (gimple_assign_rhs2 (stmt))
+      && tree_to_shwi (gimple_assign_rhs2 (stmt)) == 2)
+    return true;
+  return false;
+}
+
+/* Returns true if STMT is equivalent to x >> 1.  */
+
+static bool
+is_rshift_by_1 (gassign *stmt)
+{
+  if (!TYPE_UNSIGNED (TREE_TYPE (gimple_assign_lhs (stmt))))
+    return false;
+  if (gimple_assign_rhs_code (stmt) == RSHIFT_EXPR
+      && integer_onep (gimple_assign_rhs2 (stmt)))
+    return true;
+  if (gimple_assign_rhs_code (stmt) == TRUNC_DIV_EXPR
+      && tree_fits_shwi_p (gimple_assign_rhs2 (stmt))
+      && tree_to_shwi (gimple_assign_rhs2 (stmt)) == 2)
+    return true;
+  return false;
+}
+
 /* See comment below for number_of_iterations_bitcount.
    For c[lt]z, we have:
 
@@ -2400,14 +2432,12 @@ number_of_iterations_cltz (loop_p loop, edge exit,
 
   /* Make sure iv_2_stmt is a logical shift by one stmt:
      iv_2 = iv_1 {<<|>>} 1  */
-  if (!is_gimple_assign (iv_2_stmt)
-      || (gimple_assign_rhs_code (iv_2_stmt) != LSHIFT_EXPR
-         && (gimple_assign_rhs_code (iv_2_stmt) != RSHIFT_EXPR
-             || !TYPE_UNSIGNED (TREE_TYPE (gimple_assign_lhs (iv_2_stmt)))))
-      || !integer_onep (gimple_assign_rhs2 (iv_2_stmt)))
+  if (!is_gimple_assign (iv_2_stmt))
+    return false;
+  bool left_shift = false;
+  if (!((left_shift = is_lshift_by_1 (as_a <gassign *> (iv_2_stmt)))
+       || is_rshift_by_1 (as_a <gassign *> (iv_2_stmt))))
     return false;
-
-  bool left_shift = (gimple_assign_rhs_code (iv_2_stmt) == LSHIFT_EXPR);
 
   tree iv_1 = gimple_assign_rhs1 (iv_2_stmt);
 
@@ -2516,14 +2546,12 @@ number_of_iterations_cltz_complement (loop_p loop, edge exit,
 
   /* Make sure iv_2_stmt is a logical shift by one stmt:
      iv_2 = iv_1 {>>|<<} 1  */
-  if (!is_gimple_assign (iv_2_stmt)
-      || (gimple_assign_rhs_code (iv_2_stmt) != LSHIFT_EXPR
-         && (gimple_assign_rhs_code (iv_2_stmt) != RSHIFT_EXPR
-             || !TYPE_UNSIGNED (TREE_TYPE (gimple_assign_lhs (iv_2_stmt)))))
-      || !integer_onep (gimple_assign_rhs2 (iv_2_stmt)))
+  if (!is_gimple_assign (iv_2_stmt))
+    return false;
+  bool left_shift = false;
+  if (!((left_shift = is_lshift_by_1 (as_a <gassign *> (iv_2_stmt)))
+       || is_rshift_by_1 (as_a <gassign *> (iv_2_stmt))))
     return false;
-
-  bool left_shift = (gimple_assign_rhs_code (iv_2_stmt) == LSHIFT_EXPR);
 
   tree iv_1 = gimple_assign_rhs1 (iv_2_stmt);